April 9, 2012 -- Extreme summer temperature swings may be a health threat for people ages 65 and older, a 20-year study shows.

Those kinds of big temperature swings are becoming more common, according to some climate models.

"It means we probably should be more concerned about climate change because there may be some significant health effects directly associated with the increasing variability of weather," says researcher Joel Schwartz, PhD, a Harvard University professor of environmental epidemiology.

The new study, published in Proceedings of the National Academy of Sciences, shows that day-to-day temperature swings -- when the thermometer seesaws more than usual, catching us wearing sweatpants when shorts would feel better, and vice versa -- may be dangerous, particularly for older adults with chronic health problems.

Friends, relatives, and neighbors should try to keep a closer eye on people with chronic health problems -- not just on days with blazing heat, but also during sudden weather snaps, says Robert Glatter, MD, an emergency medicine specialist at Lenox Hill Hospital in New York.

"Watch for any changes in their daily vital signs and complaints," says Glatter, who was not involved in the study. "Make sure you're listening very carefully to their complaints."

The problem seems to be that wild temperature swings
stress the body, and many frail elders simply can't adjust.

"If a cold-front comes through and it goes from 95 to 70, you know, that's it. Your body isn't going to switch into its 70-degree mode," Schwartz says.

Temperature Check

For the study, Schwartz and his colleagues compared more than 20 years of Medicare records of people ages 65 and older with summer temperature changes over the same time period for 135 U.S. cities.

They took into account other environmental variables, too, such as air pollution and the number of parks and trees in an urban area. They also looked at other factors known to influence life expectancy, including income, education, and race.

The study found that changes in a city's average summertime temperature range of as little as 1 degree Celsius, or 1.8 degrees Fahrenheit, were linked to higher death rates for seniors with heart and lung disease and diabetes.

For each 1 degree Celsius change in the average temperature, death risk rose 4.0% for those with diabetes; 3.8% for those who'd had a previous heart attack; 3.7% for those with chronic lung disease; and 2.8% for those with heart failure.

Those are not huge increases. But spreading the risk over a large population of people, researchers say temperature swings could be responsible for as many as 14,000 premature deaths in heart attack survivors each year, for example.

Climate Change to Blame?

The researchers also found that big temperature swings are becoming more common, possibly because of climate change.

"It means we probably should be more concerned about climate change because there may be some significant health effects directly associated with the increasing variability of weather," Schwartz says.

The findings are "cause for concern," says Kim Knowlton, DrPH, a senior scientist in the Natural Resources Defense Council's health and environment program in New York. Knowlton, who was not involved in the research, says the study "points to a really important effect that hasn't been so much captured before."

Big temperature changes appeared to be most stressful for people who live in Southern as opposed to Northern states.

"Living in a warmer climate is not worse for you. But if it's a warmer climate and it has big temperature swings, then those people seem to be more susceptible than people in a climate where the summer isn't as hot and had similar-sized temperature swings," says Schwartz.

One silver lining of the study was that green space in a city seemed to reduce the risks of changing temperatures.

For every 15% increase in green surfaces within a city, researchers found that the risk of premature death for heart attack patients dropped about 2%.

"We really need to think about green space in a serious way, and planting trees on streets in urban areas, because that seems to damp down this effect," Schwartz says.